CUET Preparation Today
Case: Read the passage and answer the following questions Aldehydes and ketones are generally prepared by oxidation of primary and secondary alcohols. Dehydrogenation of alcohols gives aldehydes and ketones. Ozonolysis alkenes give aldehydes ketones or a mixture of both depending on the substitution pattern of the alkene. Aldehydes are prepared from acyl chloride, nitrile, esters and even from hydrocarbons by different kinds of oxidation. Ketones are prepared from benzene or its derivatives through Friedel-Crafts acylation reaction. Carboxylic acids are prepared from aldehydes and ketones on oxidation. Nitriles are hydrolysed to amides and then to carboxylic acids. It is even prepared using Grignard’s reagent. |
Nitriles are reduced to corresponding imine with stannous chloride in the presence of hydrochloric acid, which on hydrolysis give corresponding aldehyde. What is the reaction called? |
Wurtz reaction Rosenmund reaction Stephen reaction Sandmeyers reaction |
Stephen reaction |
The correct answer is option 3. Stephen reaction The reaction described is the Stephen reaction (also known as the Stephen aldehyde synthesis). It is a specific method used to convert nitriles into aldehydes through a two-step process involving an imine intermediate. Understanding the Mechanism 1. Reduction to Imine: The nitrile $(R-CN)$ reacts with stannous chloride $(SnCl_{2})$ in the presence of gaseous hydrochloric acid $(HCl)$. This reduces the triple bond to a double bond, forming an iminium salt (often referred to simply as an imine). $R-CN + SnCl_{2} + HCl \rightarrow R-CH=NH \cdot HCl$ 2. Hydrolysis to Aldehyde: The resulting imine is then hydrolyzed with warm water to yield the corresponding aldehyde and ammonium chloride. $R-CH=NH \cdot HCl + H_{2}O \rightarrow R-CHO + NH_{4}Cl$ Why the other options are incorrect:
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